It has been long recognized by clinicians that porcelain restorations can cause a significant amount of wear and abrasion of the opposing natural tooth structure. The literature suggests that the leucite component of dental porcelain may be an important factor in the abrasiveness of dental porcelain. The long term goal of this work is to define the compositional and microstructural parameters which are critical in the formulation of dental ceramics that have abrasive wear properties compatible with natural teeth. The objectives of this research proposal are: 1) to develop a test methodology for specifically measuring wear rates of natural tooth enamel when exposed to dental porcelain. and 2) To evaluate the effect of changes in corn position and microstructure of feldspathic dental porcelain (specifically, the volume fraction of leucite) on the abrasive wear of the dental porcelain against natural tooth enamel. The MLS servohydaulic artificial mouth is to be used to simulate the chewing action of tooth enamel against five experimental porcelain compositions, and three commercially available feldspathic porcelain products. Volume fractions of leucite in the experimental compositions will be controlled at 0, 10. 20, 30, and 40%. Samples of porcelain resembling an upper central incisor will be abraded against natural lower incisors. The tooth enamel and porcelain samples will be measured for volume loss due to abrasive wear at intervals corresponding to six months, one year, two years and three years of natural chewing activity. The results of the volume loss measurements for each porcelain/ tooth enamel combination will be compared statistically to determine if the wear of enamel is dependent on the volume fraction of leucite in the porcelain. If the central hypothesis is true (i.e., if the wear rate of the enamel is a function of the volume fraction of leucite in feldspathic porcelain), this new information will be useful in the design of dental porcelain compositions which have wear characteristics more compatible with the opposing tooth structure.